attempting to measure N2pc response. First, the stimuli should be identical in all conditions, and the experimenter should only manipulate instructions for directing attention across conditions; this precludes the possibility that stimulus features drive ERP effects rather than focused attention. Second, the target should be easy to find, usually via "pop-out." The goal is to minimize the variability in search times and N2pc latency, resulting in a much clearer signal when the waveforms are averaged together over multiple trials. An example experiment for eliciting the N2pc that follows the critical principles above might proceed as follows: Subjects see an array of upright and inverted T's. One T is red, and one T is green, but the rest are black (thus fulfilling the first criterion of easy-to-find targets). Subjects are told to attend to either the red T's or the green T's at the beginning of the experiment and report whether that letter is upright or inverted (thus fulfilling the second criterion that attention should not be confounded with stimulus characteristics). We should expect to see an N2pc contralateral to the side of the screen the attended letter appeared. Functional sensitivity Amplitude The N2pc is primarily sensitive to the directional focus of attention over time. However, research has found a variety of factors that modulate N2pc response. N2pc amplitude is sensitive to factors related to increasing demands on focused attention. When non-target stimuli closely resemble the target (e.g., when targets are defined by size, but the size difference between targets and distractors is very small), they elicit an N2pc of lower amplitude than a target stimulus When targets are defined by a conjunction of features (e.g., blue, horizontal bar) rather than a single feature (e.g., blue bar), they elicit a larger N2pc, which may reflect a greater demand on attention to identify the target. In a dual-task situation where subjects focus on a demanding primary task while performing target detection as a secondary task, the N2pc only appears in response to detecting targets defined by conjunctions of features. Again, the greater attentional demands of conjunction-based targets relative to feature-based targets may be responsible. N2pc amplitude increases as distractors appear closer to the target, which increases the need to focus on the target while filtering the distractors (but also see Mazza et al., 2009, who found conflicting results). When subjects have to indicate where a target is located, they exhibit a larger